Spatial diversity is typically a function of the number and placement of transmit and receive antennas relative to a transmitter and receiver. Systems employing spatial diversity with multiple transmit and receive antennas are generally referred to as multiple-input multiple-output (MIMO) systems. Accordingly, a transmitting device will have M transmit antennas, and the receiving device will have N receive antennas. A common MIMO transmission technique transmits different data from different transmit antennas. This transmission technique, which is often referred to as V-BLAST (Vertical-Bell Laboratories Layered Space Time), increases system throughput for systems having sufficient diversity available. Further information related to BLAST techniques can be found in Siavash M. Alamouti, “A Simple Transmit Diversity Technique for Wireless Communications,” IEEE J. Select. Areas Commun., vol. 16, pp. 1451–1458, Oct. 1998; G. J. Foschini, “Layered Space-time Architecture for Wireless Communications in a Fading Environment when Using Multi-element antennas,” Bell Labs Tech. J., pp. 41–59, Autumn 1996; G. D. Golden, G. J. Foschini, R. A. Valenzuela, and P. W. Wolniansky, “Detection Algorithm and Initial Laboratory Results Using V-BLAST Space-time Communication Architecture,” Electronics Letters, vol. 35, pp. 14–16, Jan. 1999; and P. W. Wolniansky, G. J., Foschini, G. D. Golden, and R. A. Valenzuela, “V-BLAST: An Architecture for Realizing Very High Data Rates Over the Rich-scattering Wireless Channel,” Proc. IEEE ISSSE-98, Pisa, Italy, Sep. 1998, pp. 295–300, which are incorporated herein by reference.
Interference and fading are significant impediments to achieving high data rates in today's wireless communication systems and is particularly problematic in MIMO systems. Given the tendency for channel conditions to sporadically and significantly fade, communication resources are conservatively allocated, leaving excessive amounts of communication resources unused most of the time.
In cellular embodiments, the transmitter at a base station will typically be associated with more antennas than are used to receive transmitted signals at the receiver of a user element. As the user element moves or environmental conditions change, the channel conditions between any one of the transmit antennas and the receive antennas may significantly change. As such, at any given moment there are communication channels between the transmit and receive antennas that are better than others. In an effort to capitalize on those channels providing better transmission conditions, there is a need for a technique to facilitate transmissions from the transmitter to the receiver in a manner taking advantage of these more favorable channel conditions. Further, there is a need to provide signal reinforcement in the communication channel to provide a beam-forming effect in an efficient manner in a MIMO system, and in particular in a MIMO system incorporating BLAST encoding and decoding.